Liquid crystal display

ABSTRACT

A liquid crystal display (LCD) which can provide uniform vertical and horizontal visibility while improving lateral visibility is provided. The LCD includes a first insulating substrate, first and second gate lines which are formed on the first insulating substrate, and a data line which is insulated from the first and second gate lines and intersects the first and second gate lines. The LCD also includes first and second thin film transistors (TFTs) which are formed in each pixel and are connected to the first and second gate lines, respectively, and to the data line, first sub-pixel electrodes which are connected to the first TFT, and a second sub-pixel electrode which is separated from the first sub-pixel electrodes by predetermined gaps and is connected to the second TFT. The LCD includes a second insulating substrate which faces the first insulating substrate, a common electrode which is formed on the second insulating substrate and comprises a plurality of domain dividers, and a liquid crystal layer which is interposed between the first and second insulating substrates, wherein a display region of the second sub-pixel electrode is divided into 4 domain groups by the domain dividers, and the 4 domain groups have substantially the same area.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2005-0066014 filed on Jul. 20, 2005 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure relates to a display device, and moreparticularly, to a liquid crystal display (LCD).

2. Discussion of the Related Art

A liquid crystal display (LCD) is one of the most widely used flat paneldisplays. An LCD includes two panels provided with field-generatingelectrodes such as pixel electrodes and a common electrode and a liquidcrystal (LC) layer interposed therebetween. The LCD displays images byapplying voltages to the field-generating electrodes to generate anelectric field in the LC layer, which determines orientations of LCmolecules in the LC layer to adjust polarization of incident light.

Among the LCDs, a vertical alignment (VA) mode LCD, which aligns LCmolecules such that the long axes of the LC molecules are perpendicularto the panels in the absence of an electric field, exhibits a highcontrast ratio and wide reference viewing angle. The reference viewingangle is defined as a viewing angle resulting in a contrast ratio equalto 1:10 or as a limit angle for the inversion in luminance between thegrays.

The wide viewing angle of the VA mode LCD can be realized through theuse of cutouts in the field-generating electrodes and/or protrusions onthe field-generating electrodes. Since the cutouts and the protrusionsinfluence the tilt directions of the LC molecules, the tilt directionscan be distributed into several directions by using the cutouts and theprotrusions such that the reference viewing angle is widened.

However, the VA mode LCD has relatively poor lateral visibility comparedwith front visibility. For example, a patterned VA (PVA) mode LCD havingthe cutouts can result in an image that becomes bright as a viewer movesaway from the front vantage point, and in the worse case, the luminancedifference between high grays vanishes such that the images cannot beperceived.

In addition, in LCDs, a pixel region is divided into a plurality ofdomains by cutouts or protrusions formed in or on a pixel electrode anda common electrode. However, the domains are likely to have differentareas, and thus, it is difficult to provide uniform vertical andhorizontal visibility.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide an LCD which can provideuniform vertical and horizontal visibility while improving lateralvisibility.

According to an embodiment of the present invention, there is provided aliquid crystal display (LCD) including a first insulating substrate,first and second gate lines which are formed on the first insulatingsubstrate, a data line which is insulated from the first and second gatelines and intersects the first and second gate lines, first and secondthin film transistors (TFTs) which are formed in each pixel and areconnected to the first and second gate lines, respectively, and to thedata line, first sub-pixel electrodes which are connected to the firstTFT, a second sub-pixel electrode which is separated from the firstsub-pixel electrodes by predetermined gaps and is connected to thesecond TFT, a second insulating substrate which faces the firstinsulating substrate, a common electrode which is formed on the secondinsulating substrate and comprises a plurality of domain dividers, and aliquid crystal layer which is interposed between the first and secondinsulating substrates, wherein a display region of the second sub-pixelelectrode is divided into 4 domain groups by the domain dividers, andthe 4 domain groups have substantially the same area.

According to another embodiment of the present invention, a liquidcrystal display (LCD) device comprises a first substrate, a first gateline and a second gate line formed on the first substrate, a data lineintersecting the first and second gate lines, a first thin filmtransistor and a second thin film transistor formed in each pixel of aplurality of pixels and connected to the first and second gate lines,respectively, and to the data line, a first sub-pixel electrodeconnected to the first thin film transistor, a second sub-pixelelectrode separated from the first sub-pixel electrode by apredetermined gap and connected to the second thin film transistor, asecond substrate facing the first substrate, and a common electrodeformed on the second substrate and comprising a plurality of domaindividers, wherein a display region of the second sub-pixel electrode isdivided into a plurality of domain groups according to a shape of thesecond sub-pixel electrode and the domain dividers, and each of theplurality of domain groups have substantially the same area.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention can be understood in more detailfrom the following descriptions taken in conjunction with theaccompanying drawings in which:

FIGS. 1A through 1C are block diagrams of an LCD according to anexemplary embodiment of the present invention;

FIG. 2 is an equivalent circuit diagram of a pixel of an LCD accordingto an exemplary embodiment of the present invention;

FIG. 3 is an equivalent circuit diagram of a sub-pixel of an LCDaccording to an exemplary embodiment of the present invention;

FIG. 4A is a layout view of a lower display panel of an LCD according toan exemplary embodiment of the present invention;

FIG. 4B is a layout view of an upper display panel of an LCD accordingto an exemplary embodiment of the present invention;

FIG. 4C is a layout view of an LCD including the display panel of FIG.4A and the display panel of FIG. 4B according to an exemplary embodimentof the present invention;

FIG. 5 is an enlarged layout view of a sub-pixel electrode of FIG. 4C;

FIG. 6A is a layout view of a lower display panel of an LCD according toanother exemplary embodiment of the present invention;

FIG. 6B is a layout view of an LCD including an upper display panel andthe display panel of FIG. 6A according to another exemplary embodimentof the present invention; and

FIG. 7 is an enlarged layout view of a sub-pixel electrode of FIG. 6B.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in many different forms and shouldnot be construed as being limited to the embodiments set forth herein.

FIGS. 1A through 1C are block diagrams of an LCD according to anexemplary embodiment of the present invention. FIG. 2 is an equivalentcircuit diagram of a pixel of an LCD according to an exemplaryembodiment of the present invention. FIG. 3 is an equivalent circuitdiagram of a sub-pixel of an LCD according to an exemplary embodiment ofthe present invention.

Referring to FIGS. 1A through 1C, an LCD according to an exemplaryembodiment of the present invention includes a liquid crystal panelassembly 300, a data driving unit 500 and a gate driving unit 400 (or apair of gate driving units 400 a and 400 b) which are connected to theliquid crystal panel assembly 300. A gray-scale voltage generation unit800 is connected to the data driving unit 500. A signal control unit 600controls the gate driving unit 400 (or the gate driving units 400 a and400 b) and the data driving unit 500.

The liquid crystal panel assembly 300 includes a plurality of displaysignal lines and a plurality of pixels PX which are connected to thedisplay signal lines and are arranged in a matrix format. Referring toFIG. 3, the liquid crystal panel assembly 300 may include a lowerdisplay panel 100 and an upper display panel 200 which face each otherand a liquid crystal layer 3 which is interposed between the lower andupper display panels 100 and 200.

The display signal lines are formed on the lower display panel 100 andinclude a plurality of gate lines G_(la) through G_(na) and G_(lb)through G_(nb), which transmit gate signals, and a plurality of datasignals D₁ through D_(m) which transmit data signals. The gate linesG_(la) through G_(na) and G_(lb) through G_(nb) substantially extend ina transverse direction and are parallel to one another, while the datalines D_(l) through D_(m) substantially extend in a longitudinaldirection and are parallel to one another.

FIG. 2 is an equivalent circuit diagram of a pixel PX of an LCDaccording to an exemplary embodiment of the present invention includinggate lines GLa and GLb, a data line DL, and a storage electrode line SL,which is substantially parallel to the gate lines GLa and GLb.

Referring to FIG. 2, the pixel PX comprises a pair of sub-pixels PXa andPXb. The sub-pixels PXa and PXb include switching devices Qa and Qb,respectively, liquid crystal capacitors Clca and Clcb, respectively, andstorage capacitors Csta and Cstb, respectively. The switching devices Qaand Qb are connected to the gate lines GLa and GLb, respectively, andare connected to the data line DL. The liquid crystal capacitors Clcaand Clcb are connected to the switching devices Qa and Qb, respectively.The storage capacitors Csta and Cstb are connected to the switchingdevices Qa and Qb, respectively, and are connected to the storageelectrode line SL. The pixel PX may optionally include the storagecapacitors Csta and Cstb. If the pixel PX does not include the storagecapacitors Csta and Cstb, the storage electrode line SL can be omitted.

Referring to FIG. 3, a switching device Q of a sub-pixel PE includes athin film transistor (TFT) formed on the lower display panel 100 and isa three-end portion device including a control end portion connected toa gate line GL, an input end portion connected to a data line DL, and anoutput end portion connected to a liquid crystal capacitor C_(lc) and astorage capacitor C_(st).

The sub-pixel electrode PE of the lower display panel 100 and a commonelectrode CE of an upper display panel 200 function as two terminals ofthe liquid crystal capacitor C_(lc), and the liquid crystal layer 3interposed between the sub-pixel electrode PE and the common electrodeCE serves as a dielectric material. The sub-pixel electrode PE isconnected to the switching device Q. The common electrode CE is formedon a surface of the upper display panel 200, for example, a frontsurface, and a common voltage Vcom is applied to the common electrodeCE. The common electrode CE may be formed on the lower display panel100, in which case, the sub-pixel electrode PE or the common electrodeCE may be shaped as a line or a strip.

The storage capacitor C_(st) is an auxiliary capacitor for the LCcapacitor C_(lc). The storage capacitor C_(st) includes the pixelelectrode PE and a separate signal line (not shown), which is providedon the lower panel 100. The separate signal line overlaps the pixelelectrode PE via an insulator, and is supplied with a predeterminedvoltage such as the common voltage Vcom. Alternatively, the storagecapacitor C_(st) includes the pixel electrode PE and an adjacent gateline called a previous gate line, which overlaps the pixel electrode PEvia an insulator.

For a color display, each pixel represents one of three primary colorssuch as red, green and blue (R, G and B) colors (spatial division) orsequentially represents the three primary colors in time (temporaldivision), so as to obtain a desired color. FIG. 3 shows an example ofthe spatial division in which each pixel includes a color filter CFrepresenting one of the three primary colors in an area of the upperpanel 200. The color filter CF may also be provided on or under thepixel electrode PE of the lower panel 100.

Referring to FIGS. 1A through 1C, the gate driving unit 400 (or the gatedriving units 400 a and 400 b) is connected to the gate lines G_(la)through G_(na) and G_(lb) through G_(nb) and applies gate signalsconsisting of a gate-on voltage Von and a gate-off voltage Voff appliedfrom an external circuit to the gate lines G_(la) through G_(na) andG_(lb) through G_(nb). In detail, referring to FIG. 1A, the gate drivingunits 400 a and 400 b are located on the left and right sides,respectively, of the liquid crystal panel assembly 300 and are connectedto the odd-numbered gate lines G_(la) through G_(na) and theeven-numbered gate lines G_(lb) through G_(nb), respectively. Referringto FIGS. 1B and 1C, the gate driving unit 400 is located on one side ofthe liquid crystal panel assembly 300 and is connected to all of thegate lines G_(la) through G_(na) and G_(lb) through G_(nb). Referring toFIG. 1C, the gate driving unit 400 includes two driving circuits 401 and402 which are connected to the odd-numbered gate lines and theeven-numbered gate lines, respectively.

The gray-scale voltage generation unit 800 generates two sets ofgray-scale voltages (or reference gray-scale voltage sets) which arerelated to the transparencies of the pixels PX. The two gray-scalevoltage sets are independently provided to a pair of sub-pixels of eachpixel PX. Each of the two gray-scale voltage sets includes positivepolarity level and negative polarity level with respect to the commonvoltage Vcom, but the embodiments of the present invention are notrestricted thereto. Alternatively, the gray-scale voltage generationunit 800 may generate only one gray-scale voltage set, rather thangenerating two gray-scale voltage sets.

The data driving unit 500 is connected to the data lines D_(l) throughD_(m) of the liquid crystal panel assembly 300, selects one of the twogray-scale voltage sets generated by the gray-scale voltage generationunit 800, and applies one of a plurality of gray-scale voltages includedin the selected gray-scale voltage set to the pixels PX as a datavoltage. If the gray-scale voltage generation unit 800 provides only areference gray-scale voltage, instead of providing a set of voltages forall gray scales, the data driving unit 500 generates a plurality ofreference voltages for all gray scales by dividing the reference grayscale and selects one of the reference voltages as a data voltage.

The gate driving unit 400 (or the gate driving units 400 a and 400 b)and/or the data driving unit 500 may be formed as an integrated chip onwhich a plurality of driving circuits are integrated. The gate drivingunit 400 (or the gate driving units 400 a and 400 b) and/or the datadriving unit 500 may be directly mounted on the liquid crystal panelassembly 300. Alternatively, the gate driving unit 400 (or the gatedriving units 400 a and 400 b) and/or the data driving unit 500 may bemounted on a flexible printed circuit film (not shown), and then theresulting structure may be mounted on the liquid crystal panel assembly300 as a tape carrier package. Alternatively, the gate driving unit 400(or the gate driving units 400 a and 400 b) and/or the data driving unit500 may be integrated on the liquid crystal panel assembly 300 togetherwith the display signal lines G_(la) through G_(na), G_(lb) throughG_(nb) and D_(l) through D_(m) and a switching device Q of a TFT.

The signal control unit 600 controls the gate driving unit 400 (or thegate driving units 400 a and 400 b) and the data driving unit 500.

LCDs according to exemplary embodiments of the present invention willnow be described in detail with reference to FIGS. 4A through 7.

First, FIGS. 4A through 4C and 5 are diagrams illustrating an LCDaccording to an exemplary embodiment of the present invention. The LCDincludes a lower display panel, an upper display panel, which faces thelower display panel, and a liquid crystal layer which is interposedbetween the lower and upper display panels.

A lower display panel of the LCD according to an exemplary embodiment ofthe present invention will now be described in detail with reference toFIGS. 4A through 4C.

Referring to FIGS. 4A through 4C, a pair of gate lines, e.g., first andsecond gate lines 22 a and 22 b, and a storage electrode line 28, areformed on an insulating substrate, which is formed of a transparentmaterial, such as glass.

The first and second gate lines 22 a and 22 b extend substantially in atransverse direction to transmit gate signals and are physically andelectrically spaced apart from each other. The first and second gatelines 22 a and 22 b are located on opposite sides of a pixel, forexample, the upper and lower sides, respectively, of a pixel. A pair ofelectrodes, e.g., first and second gate electrodes 26 a and 26 b, areformed as branches of the first and second gate lines 22 a and 22 b,respectively. A first gate line end portion 24 a is formed at one end ofthe first gate line 22 a, and a second gate line end portion 24 b isformed at one end of the second gate line 22 b. The first and secondgate line end portions 24 a and 24 b receive gate signals from anotherlayer or from external circuits and transmit the gate signals to thefirst and second gate lines 22 a and 22 b, respectively. The first andsecond gate line end portions 24 a and 24 b are formed wider than thefirst and second gate lines 22 a and 22 b so as to effectively connectthe first and second gate lines 22 a and 22 b to external circuits. Thefirst and second gate line end portions 24 a and 24 b are located on theleft and right sides, respectively, of a pixel region, as illustrated inFIG. 4A. Alternatively, for example, the first and second gate line endportions 24 a and 24 b may be all located on one side of a pixel region,for example, on either the left or right sides of the pixel region.

As shown in FIGS. 4A and 4C, the storage electrode line 28 extends alonga horizontal direction. A storage electrode 29 is formed on the storageelectrode line 28 and is wider than the storage electrode line 28. Inthe present embodiment, the storage electrode line 28 crosses the middleof the pixel region. The shapes and arrangement of the storage electrodeline 28 and the storage electrode 29 may vary.

The first and second gate lines 22 a and 22 b and the storage electrodeline 28 are preferably made of Al containing metal such as Al and Alalloy, Ag containing metal such as Ag and Ag alloy, Cu containing metalsuch as Cu and Cu alloy, Mo containing metal such as Mo and Mo alloy,Cr, Ti and/or Ta. In addition, the first and second gate lines 22 a and22 b and the storage electrode line 28 may have a multi-layeredstructure including two conductive films (not shown) having differentphysical characteristics. One of the two conductive films is preferablymade of a low resistivity metal including Al containing metal, Agcontaining metal, and/or Cu containing metal for reducing signal delayor voltage drop in the first and second gate lines 22 a and 22 b and thestorage electrode line 28. The other conductive film is preferably madeof material such as a Mo containing metal, Cr, Ta and/or Ti, which havegood physical, chemical, and electrical contact characteristics withother materials such as indium tin oxide (ITO) or indium zinc oxide(IZO). A good exemplary combination is a lower Cr film and an upper Alfilm or a lower Al film and an upper Mo film. However, the first andsecond gate lines 22 a and 22 b and the storage electrode line 28 may bemade of various metals or conductors.

A gate insulation layer (not shown) formed of, for example, siliconnitride (SiN_(x)), is formed on the first and second gate lines 22 a and22 b and the storage electrode line 28.

Semiconductor layers 40 a and 40 b formed of, for example, hydrogenatedamorphous silicon or porous silicon, are formed on the gate insulationlayer. The semiconductor layers 40 a and 40 b may have various shapessuch as island shapes or line shapes. In an illustrative embodiment, forexample, the semiconductor layers 40 a and 40 b may be formed in anisland shape. When the semiconductor layers 40 a and 40 b are formed ina line shape, they may be disposed under the data line 62 and extended.

An ohmic contact layer (not shown) formed of, for example, silicide orn+hydrogenated amorphous silicon doped with a high concentration ofn-type impurities, is formed on the semiconductor layers 40 a and 40 b.Ohmic contacts are provided on the semiconductor layers 40 a and 40 b inpairs.

The data line 62 and first and second drain electrodes 66 a and 66 b areformed on the ohmic contact layer and the gate insulation layer.

The data line 62 extends substantially along a longitudinal direction,intersects the first and second gate lines 22 a and 22 b and the storageelectrode line 28, and transmits a data voltage. First and second sourceelectrodes 65 a and 65 b are formed on the data line 62 and extendtoward the first and second drain electrodes 66 a and 66 b,respectively. In addition, a data line end portion 68 is formed at oneend of the data line 62. The data line end portion 68 receives a datasignal from another layer or an external source and transmits the datasignal to the data line 62. The data line end portion 68 is formed widerthan the data line 62 so as to effectively connect the data line 62 toan external circuit.

The data line 62, the first and second source electrodes 65 a and 65 band the first and second drain electrodes 66 a and 66 b are preferablymade of refractory metal such as Cr, a metal containing Mo, Ta, and/orTi. Also, the data line 62, the first and second source electrodes 65 aand 65 b and the first and second drain electrodes 66 a and 66 b mayhave a multilayered structure including a lower refractory metal filmand a low-resistivity upper film (not shown). Examples of themulti-layered structure include a double-layered structure having anupper Cr film and an upper Al film or a lower Al film and an upper Mofilm, and a triple-layered structure having a lower Mo film, anintermediate Al film, and an upper Mo film.

The first and second source electrodes 65 a and 65 b at least partiallyoverlap the semiconductor layers 40 a and 40 b, respectively. The firstand second drain electrodes 66 a and 66 b are opposite to and face thefirst and second source electrodes 65 a and 65 b, with respect to thegate electrodes 26 a and 26 b, respectively, and at least partiallyoverlap with the semiconductor layers 40 a and 40 b, respectively. Theohmic contacts are interposed between the underlying semiconductorlayers 40 a, 40 b and the overlying first and second source electrodes65 a, 65 b and first and second drain electrodes 66 a, 66 b to reducethe contact resistance between semiconductor layers and the source anddrain electrodes.

The first and second drain electrodes 66 a and 66 b include strip-typeend portions overlapping with the semiconductor layers 40 a and 40 b.Drain electrode extensions 67 a and 67 b extend from the strip-type endportions, are wider than the strip-type end portions, and overlap thestorage electrode 29.

Each of the first and second source electrodes 65 a and 65 b areseparated into two branches and surround the strip-type end portions ofthe first and second drain electrodes 66 a and 66 b, respectively.

A passivation layer (not shown) is formed on the data line 62, the firstand second drain electrodes 66 a and 66 b, and exposed portions of thesemiconductor layers 40 a and 40 b. The passivation layer is preferablymade of an inorganic insulator such as silicon nitride or silicon oxide,a flat photosensitive organic material, or a low dielectric insulatingmaterial such as a-Si:C:O and a-Si:O:F formed by plasma enhancedchemical vapor deposition (PECVD). In addition, the passivation layermay be formed as a double layer including a lower inorganic layer and anupper organic layer so as to provide organic layer characteristics andeffectively protect the exposed portions of the semiconductor layers 40a and 40 b.

Contact holes 78, 76 a, and 76 b are formed through the passivationlayer so that the data line end portion 68 and the drain electrodeextensions 67 a and 67 b can be exposed through the contact holes 78, 76a, and 76 b, respectively. Contact holes 74 a and 74 b are formedthrough the passivation layer and the gate insulation layer so that thefirst and second gate line end portions 24 a and 24 b can be exposedthrough the contact holes 74 a and 74 b, respectively. First and secondsub-pixel electrodes 82 a and 82 b are formed to be electricallyconnected to the first and second drain electrodes 66 a and 66 b,respectively, through the contact holes 76 a and 76 b, respectively.Auxiliary gate line end portions 86 a and 86 b and an auxiliary dataline end portion 88 are formed on the passivation layer and areconnected to the first and second gate line end portions 24 a and 24 band the data line end portion 68, respectively, through the contactholes 74 a, 74 b, and 78, respectively. The first and second sub-pixelelectrodes 82 a and 82 b and the auxiliary gate and data line endportions 86 a, 86 b, 88 are preferably made of a transparent conductorsuch as ITO or IZO and/or a reflective conductor such as Al.

The first and second sub-pixel electrodes 82 a, 82 b are physically andelectrically connected to the first and second drain electrodes 66 a, 66b through the contact holes 76 a, 76 b such that the first and secondsub-pixel electrodes 82 a, 82 b receive the data voltages from the firstand second drain electrodes 66 a, 66 b.

Electric fields are generated between the first and second sub-pixelelectrodes 82 a, 82 b supplied with the data voltages and the commonelectrode of the upper display panel. The electric fields influence anorientation of liquid crystal molecules in the LC layer between thefirst and second sub-pixel electrodes 82 a, 82 b and the commonelectrode.

As described above, the first sub-pixel electrode 82 a forms the liquidcrystal capacitor Clca with the common electrode CE, and the secondsub-pixel electrode 82 b forms the liquid crystal capacitor Clcb withthe common electrode CE. Accordingly, even after the switching devicesQa and Qb are turned off, the first and second sub-pixel electrodes 82 aand 82 b can maintain a predetermined voltage level.

In order to enhance storage capacity, the storage capacitor Csta and theliquid crystal capacitor Clca are connected in parallel to each other,and the storage capacitor Cstb and the liquid crystal capacitor Clcb areconnected in parallel to each other. The storage capacitors Csta andCstb are formed by arranging the first and second sub-pixel electrodes82 a and 82 b or the first and second drain electrodes 66 a and 66 bconnected to the first and second sub-pixel electrodes 82 a and 82 b,respectively, to overlap the storage electrode line 28.

The first and second sub-pixel electrodes 82 a and 82 b are separatedfrom each other by gaps 83. The gaps 83 may have a rectangular shape.The second sub-pixel electrodes 82 b are V-shaped and are located in themiddle of a pixel region. The first sub-pixel electrodes 82 a are formedin portions of the pixel region where the second sub-pixel electrode 82b is not formed. The gaps 83 include a gap that forms an angle of about45 degrees with a transmission axis 1 of a polarizing plate and a gapthat forms an angle of about −45 degrees with the transmission axis 1 ofthe polarizing plate. Therefore, upper oblique portions of the secondsub-pixel electrode 82 b form an angle of −45 degrees with thetransmission axis 1 of the polarizing plate, and lower oblique portionsof the second sub-pixel electrode 82 b form an angle of 45 degrees withthe transmission axis 1 of the polarizing plate. A plurality of cutouts84 may be formed in the first sub-pixel electrodes 82 a in thelongitudinal directions of the respective gaps 83. Alternatively to, orin addition to the cutouts 84, a plurality of protrusions may be formedon the first sub-pixel electrodes 82 a in the longitudinal directions ofthe respective gaps 83 (hereinafter referred to as oblique directions).The sizes and shapes of the first and second sub-pixel electrodes 82 aand 82 b and the cutouts 84 (or the protrusions) may vary in a varietyof manners according to design factors.

Different gray-scale voltages are applied to the first and secondsub-pixel electrodes 82 a and 82 b. For example, a gray-scale voltagewhich is lower than a reference gray-scale voltage may be applied to thefirst sub-pixel electrodes 82 a, and a gray-scale voltage which ishigher than the reference gray-scale voltage may be applied to thesecond sub-pixel electrode 82 b. Assuming that a ratio of an area of thefirst sub-pixel electrodes 82 a to an area of the second sub-pixelelectrodes 82 b is about 2:1, the lateral visibility of an LCD includingthe first and second sub-pixel electrodes 82 a and 82 b can beconsiderably improved by applying different gray-scale voltages to thefirst and second sub-pixel electrodes 82 a and 82 b in theabove-described manner.

The auxiliary gate line end portions 86 a and 86 b and the data line endportion 88 are connected to the first and second gate line end portions24 a and 24 b and the data line end portion 68, respectively, throughthe contact holes 74 a, 74 b, and 78, respectively. The auxiliary gateline end portions 86 a and 86 b and the data line end portion 88 areused for connecting external devices to the gate line end portions 24 aand 24 b and the data line end portion 68.

An alignment layer (not shown) for aligning a liquid crystal layer isformed on the first and second sub-pixel electrodes 82 a and 82 b, theauxiliary gate line end portions 86 a and 86 b, and the data line endportion 88.

An upper display panel of the LCD according to an exemplary embodimentof the present invention will now be described in detail with referenceto FIGS. 4B and 4C.

Referring to FIGS. 4B and 4C, a black matrix (not shown), color filters(not shown), e.g., red, green, and blue filters, and a common electrode90 are formed on an insulating substrate, which is formed of atransparent material, such as glass. The common electrode 90 is formedof a transparent material, such as ITO or IZO. The black matrixcorresponds to the first and second gate lines 22 a and 22 b, the dataline 62, and the switching devices Qa and Qb. The black matrix may beformed in various shapes. The black matrix prevents light leakage fromoccurring near the first and second sub-pixel electrodes 82 a and 82 band the switching devices Qa and Qb.

The common electrode 90 corresponds to the first and second sub-pixelelectrodes 82 a and 82 b and includes a plurality of cutouts 92 (and/ora plurality of protrusions). Here, the cutouts 92 (or the protrusions)comprise oblique portions which form an angle of −45 degrees or 45degrees with the transmission axis 1 of the polarizing plate. Asdescribed above, the first and second sub-pixel electrodes 82 a and 82b, like the common electrode 90, include the cutouts 84 (or theprotrusions).

An alignment layer (not shown) for aligning a liquid crystal layer maybe formed on the common electrode 90.

FIG. 4C is a layout view of an LCD including the lower display panel ofFIG. 4A and the upper display panel of FIG. 4B. Referring to FIG. 4C,the oblique portions of the cutouts 92 of the common electrode 90 arearranged among the gaps 83 and the cutouts 84 (or the protrusions) ofthe first sub-pixel electrodes 82 a. The relationship between thecutouts 92 of the common electrode 90 and the second sub-pixel electrode82 b will be described in detail with reference to FIG. 5.

An architecture for the LCD according to an exemplary embodiment of thepresent invention can be formed by vertically aligning the lower displaypanel of FIG. 4A and the upper display panel of FIG. 4B with each otherand coupling them with liquid crystal material interposed therebetween.When the lower display panel of FIG. 4A and the upper display panel ofFIG. 4B are vertically aligned with each other, a display region of apixel is divided into a plurality of domains by the gaps 83, the cutouts84 of the first sub-pixel electrodes 82 a, and the cutouts 92 of thecommon electrode 90. As a result, a reference viewing angle is widenedand lateral visibility is improved. The gaps and the cutouts 94 and 92(or the protrusions) may be referred to as domain dividers.

The LCD according to an exemplary embodiment of the present inventioncan include the architecture illustrated in FIG. 4B, and also includeother elements, such as a polarizing plate and a backlight assembly. Apolarizing plate may be installed on either side of the architecture insuch a manner that a first transmission axis is parallel to the gateline 22 and a second transmission axis is perpendicular to the gate line22.

In the LCD according to an exemplary embodiment of the presentinvention, a liquid crystal in each of a plurality of domains of a pixeltilts perpendicularly to the gaps 83 or the cutouts 92 when an electricfield is applied thereto. Thus, the liquid crystal in each of thedomains forms an angle of about 45 degrees or −45 degrees with atransmission axis of a polarizing plate. A lateral electric field formedin each of the gaps 83 or the cutouts 92 facilitates the alignment ofliquid crystal molecules in each domain.

A plurality of domains can be divided into, for example, 4 domain groupsaccording to the direction in which a liquid crystal in each of thedomains tilts. If the domain groups have the same area, it is possibleto provide uniform vertical and horizontal visibility. The displaycharacteristics of an LCD are determined mainly based on the secondsub-pixel electrode 82 b to which a voltage higher than a referencegray-scale voltage is applied. Therefore, if 4 domain groupsconstituting the second sub-pixel electrode 82 b have substantially thesame area, it is possible to provide uniform vertical and horizontalvisibility. An LCD according to an exemplary embodiment of the presentinvention, which is capable of providing uniform vertical and horizontalvisibility, will be described in detail with reference to FIG. 5.

FIG. 5 is an enlarged layout view of a second sub-pixel electrode ofFIG. 4C.

Referring to FIG. 5, portions of a second sub-pixel electrode 82 b aresymmetrical with respect to a storage electrode line 28 which runsacross the middle of the second sub-pixel electrode 82 b. The secondsub-pixel electrode 82 b is separated from the first sub-pixelelectrodes 82 a of FIG. 4C by the gaps 83 of FIG. 4C. The secondsub-pixel electrode 82 b is V-shaped and is located in the middle of apixel region. A cutout 92 is formed in a portion of the common electrodecorresponding to the second sub-pixel electrode 82 b. In other words, asshown in FIG. 5, the cutout 92 overlaps with the second sub-pixelelectrode 82 b, is V-shaped, and is narrower than the second sub-pixelelectrode 82 b. Therefore, the second sub-pixel electrode 82 b can bedivided into 4 domain groups, i.e., A, B, C, and D, by the storageelectrode line 28, the gaps 83 and a domain divider, such as the cutout92.

If the second sub-pixel electrode 82 b is formed such that upper andlower oblique portions of the second sub-pixel electrode 82 b aresymmetrical with respect to the storage electrode line 28, the domaingroups A and C may have substantially the same area, and the domaingroups B and D may have substantially the same area. The upper obliqueportions of the second sub-pixel electrode 82 b form an angle of −45degrees with a transmission axis of a polarizing plate, and the loweroblique portions of the second sub-pixel electrode 82 b form an angle of45 degrees with the transmission axis of the polarizing plate. Thus, inorder to result in the domain groups A and B having the same area, thewidth Wa of the domain group A must be larger than the width Wb of thedomain group B. Likewise, in order to result in the domain groups C andD having the same area, the width Wc of the domain group C must belarger than the width Wd of the domain group D. Here, the domain groupsA and C of the second sub-pixel electrode 82 b are arranged between thecutout 92 of the common electrode and the center of the pixel region. Inthis manner, the domain groups A, B, C, and D have the same area.

In order to achieve a predetermined response speed when aligning liquidcrystal molecules using domain dividers and a lateral field formed alonga predetermined direction, the domain group A or C may be formed to havea width of about 28 μm or less.

In addition, the domain group B or D may be formed to have a width ofabout 14 μm. or larger in consideration of alignment margins for upperand lower display panels.

The operation of the LCD according to an exemplary embodiment of thepresent invention will now be described in detail with reference toFIGS. 1A through 4C.

Referring to FIGS. 1A through 4C, the signal control unit 600 receivesinput image signals (R, G, B) and input control signals to control thedisplay of the input image signals. The input control signals include,for example, a vertical synchronization signal Vsync, a horizontalsynchronization signal Hsync, a main clock signal MCLK, and a dataenable signal DE. The input image signals and the input control signalsare received from an external graphic controller (not shown). The signalcontrol unit 600 appropriately processes the input image signals and theinput control signals according to the operating conditions of theliquid crystal panel assembly 300, and generates a gate control signalCONT1 and a data control signal CONT2. The signal control unit 600transmits the gate control signal CONT1 to the gate driving unit 400 (orthe gate driving units 400 a and 400 b), and transmits the data controlsignal CONT2 to the data driving unit 500.

The gate control signal CONT1 comprises a scanning initiation signal STVfor initiating scanning and at least one clock signal for controllingwhen to output the gate-on voltage Von. The gate control signal CONT1may also include an output enable signal OE for defining the duration ofthe gate-on voltage Von. Here, the clock signal included in the gatecontrol signal CONT1 may be used as a selection signal SE.

The data control signal CONT2 comprises a horizontal synchronizationsignal STH for informing the data driver 500 of a start of datatransmission for a group of pixels, a load signal LOAD for instructingthe data driver 500 to apply the data voltages to the data lines D_(l)through D_(m), and a data clock signal HCLK. The data control signalCONT2 may also include an inversion signal RVS for reversing thepolarity of the data voltages with respect to the common voltage Vcom.

In response to the data control signal CONT2 transmitted by the signalcontrol unit 600, the data driving unit 500 receives image data DAT fora pair of sub-pixels PXa and PXb, selects a gray-scale voltage for theimage data DAT, converts the image data DAT into a data voltage, andapplies the data voltage to one of the data lines D_(l) through D_(m)corresponding to the sub-pixels PXa and PXb.

The gate driving unit 400 (or the gate driving units 400 a and 400 b)applies the gate-on voltage Von to one of the gate lines G_(la) throughG_(na) and G_(lb) through G_(nb) corresponding to the sub-pixels PXa andPXb, so that switching devices Qa and Qb connected to the gate line towhich the gate-on voltage Von is applied are turned on. Accordingly, thedata voltage applied via the data line corresponding to the sub-pixelsPXa and PXb is applied to the sub-pixels PXa and PXb via the switchingdevices Qa and Qb.

A difference between the data voltage applied to the sub-pixels PXa andPXb and the common voltage Vcom is represented as a voltage across theLC capacitor Clca, which is referred to as a pixel voltage. Liquidcrystal molecules in the LC capacitor Clca have orientations dependingon a magnitude of the pixel voltage, and molecular orientations of theLC molecules determine a polarization of light passing through the LClayer. A polarizer(s) converts light polarization into a lighttransmittance.

In the LCD according to an exemplary embodiment of the presentinvention, a gate voltage is transmitted to the sub-pixels PXa and PXbby a pair of gate lines 22 a and 22 b. A pair of gray-scale voltagesets, which have different gamma curves for the sub-pixels PXa and PXbobtained from a piece of image information, are applied to thesub-pixels PXa and PXb. Thus, a gamma curve for a pixel PX comprisingthe sub-pixels PXa and PXb can be obtained by synthesizing the gammacurves for the sub-pixels PXa and PXb. It is possible to improve lateralvisibility by determining gray-scale voltages for the respectivesub-pixels PXa and PXb so that a synthesized gamma curve obtained fromthe front of an LCD is similar to a reference gamma curve for the frontof the LCD and a synthesized gamma curve obtained from either side ofthe LCD is as close as possible to the reference gamma curve.

In addition, as described above, 4 domain groups constituting the secondsub-pixel electrode 82 b are formed to have substantially the same area,thereby resulting in uniform vertical and horizontal visibility.

An LCD according to another exemplary embodiment of the presentinvention will now be described in detail with reference to FIGS. 6Athrough 7. Components having the same function as described inconnection with the embodiments shown in FIGS. 1 through 5 arerespectively identified by the same reference numerals, and theirfurther description will be omitted. FIG. 6A is a layout view of a lowerdisplay panel of an LCD according to another exemplary embodiment of thepresent invention. FIG. 6B is a layout view of an LCD including an upperdisplay panel and the lower display panel of FIG. 6A according toanother exemplary embodiment of the present invention. FIG. 7 is anenlarged layout view of a second sub-pixel electrode of FIG. 6B.

Referring to FIG. 7, the LCD is substantially the same as the LCDaccording to the embodiment of the present invention described inconnection with FIGS. 4A-4C and 5, except that, 4 domain groupsconstituting a second sub-pixel electrode 82 b, i.e., domain groups A,B, C, and D, are formed to have substantially the same width.Accordingly, the area of domain group B or D is larger than the area ofdomain groups A or C. Therefore, in order to make the domain groups A,B, C, and D have substantially the same area, a storage electrodeextension 29′ may be formed such that it extends from the storageelectrode 29 in directions of the domain groups B and D. In other words,the storage electrode extension 29′ extends toward the domain groups Band D adjacent to the storage electrode 29 so as to be overlapped withthe second sub-pixel electrode 82 b, thereby reducing the areas of thedomain groups B and D.

In the present embodiment, the storage electrode 29 having the storageelectrode extension 29′ is formed as a rotated ‘T’ shape. However, theshape formed by the storage electrode 29 and the storage electrodeextension 29′ is not restricted to the shape shown. In other words, thestorage electrode 29 and the storage electrode extension 29′ may beformed in various shapes as long as the domain groups A, B, C, and Dhave the same area.

As described above, it is possible to provide uniform vertical andhorizontal visibility by forming the 4 domain groups of the secondsub-pixel electrode 82 b divided according to orientations of liquidcrystal molecules so as to have the same area.

Accordingly, the embodiments of the present invention provide uniformvisibility in horizontal and vertical directions while improving lateralvisibility.

Although the illustrative embodiments have been described herein withreference to the accompanying drawings, it is to be understood that thepresent invention is not limited to those precise embodiments, and thatvarious other changes and modifications may be affected therein by oneof ordinary skill in the related art without departing from the scope orspirit of the invention. All such changes and modifications are intendedto be included within the scope of the invention as defined by theappended claims.

1. A liquid crystal display (LCD) device comprising: a first insulatingsubstrate; a first gate line and a second gate line formed on the firstinsulating substrate; a data line insulated from the first and secondgate lines and intersecting the first and second gate lines; a firstthin film transistor and a second thin film transistor formed in eachpixel of a plurality of pixels and connected to the first and secondgate lines, respectively, and to the data line; a first sub-pixelelectrode connected to the first thin film transistor; a secondsub-pixel electrode separated from the first sub-pixel electrode bypredetermined gaps and connected to the second thin film transistor; asecond insulating substrate facing the first insulating substrate; acommon electrode formed on the second insulating substrate andcomprising a plurality of domain dividers; and a liquid crystal layerinterposed between the first and second insulating substrates, wherein adisplay region of the second sub-pixel electrode is divided into 4domain groups according to a shape of the second sub-pixel electrode andthe domain dividers, and the 4 domain groups have substantially the samearea.
 2. The LCD of claim 1, wherein the 4 domain groups have differentwidths and lengths.
 3. The LCD of claim 2, wherein: the second sub-pixelelectrode is formed in a ‘V’ shape, the domain dividers overlap with thesecond sub-pixel electrode, and the domain dividers are narrower thanthe second sub-pixel electrode.
 4. The LCD of claim 1, furthercomprising a storage electrode line or a storage electrode, wherein the4 domain groups have the same area by varying an overlap area of thestorage electrode line or the storage electrode with the 4 domaingroups.
 5. The LCD of claim 4, wherein a storage electrode is formed onthe storage electrode line to be wider than the storage electrode lineand comprises a storage electrode extension which overlaps with at leastone of the 4 domain groups.
 6. The LCD of claim 5, wherein the storageelectrode having the storage electrode extension has a “T” shape.
 7. TheLCD of claim 1, wherein each of the 4 domain groups has a width of about28 μm or less.
 8. The LCD of claim 1, wherein each of the 4 domaingroups has a width of about 14 μm or more.
 9. A liquid crystal display(LCD) device comprising: a first substrate; a first gate line and asecond gate line formed on the first substrate; a data line intersectingthe first and second gate lines; a first thin film transistor and asecond thin film transistor formed in each pixel of a plurality ofpixels and connected to the first and second gate lines, respectively,and to the data line; a first sub-pixel electrode connected to the firstthin film transistor; a second sub-pixel electrode separated from thefirst sub-pixel electrode by a predetermined gap and connected to thesecond thin film transistor; a second substrate facing the firstsubstrate; and a common electrode formed on the second substrate andcomprising a plurality of domain dividers, wherein a display region ofthe second sub-pixel electrode is divided into a plurality of domaingroups according to a shape of the second sub-pixel electrode and thedomain dividers, and each of the plurality of domain groups havesubstantially the same area.
 10. The LCD of claim 9, wherein at leastsome of the plurality of domain groups have different dimensions. 11.The LCD of claim 9, wherein: the second sub-pixel electrode is formed ina ‘V’ shape, the domain dividers overlap with the second sub-pixelelectrode, and the domain dividers are narrower than the secondsub-pixel electrode.
 12. The LCD of claim 9, further comprising astorage electrode line or a storage electrode, wherein the plurality ofdomain groups have the same area by varying an overlap area of thestorage electrode line or the storage electrode with the plurality ofdomain groups.
 13. The LCD of claim 12, wherein a storage electrode isformed on the storage electrode line to be wider than the storageelectrode line and comprises a storage electrode extension whichoverlaps with at least one of the plurality of domain groups.
 14. TheLCD of claim 13, wherein the storage electrode having the storageelectrode extension has a “T” shape.
 15. The LCD of claim 9, whereineach of the plurality of domain groups has a width of about 28 μm orless.
 16. The LCD of claim 9, wherein each of the plurality of domaingroups has a width of about 14 μm or more.